Various resin films are used in a liquid crystal display. Among the films, a polarizer protective film is usually made from triacetylcellulose. Triacetylcellulose films have high moisture permeability. Therefore, making the triacetylcellulose film thinner tends to impair the quality of the polarizer. As liquid crystal displays are made thinner, the polarizer protective film should be improved.
As a new material of the polarizer protective film, a methacrylic resin is being researched. A film comprising a methacrylic resin is known to have its toughness increased when stretched (see Patent Document 1). However, when an ordinary methacrylic resin film is stretched, its retardation becomes greater, leading to impaired quality of an IPS liquid crystal display.
It is known that a combined use of a methacrylic resin with a polycarbonate resin or the like tends to give a film having small retardation (Patent Documents 2 to 4). However, the methacrylic resins used in these methods have undergone copolymerization with an aromatic vinyl monomer or an imide monomer for enhanced heat resistance, and are consequently poor in strength. As a result, films made with the methacrylic resins easily break and are not suitable as optical films.